Pocketed springs for use in upholstery have been known for many years, dating at least from early in the twentieth century. Assemblies of such springs as cores for mattresses or cushions are known in the industry as "Marshall" constructions or units, for the man believed to have originated the concept. See U.S. Pat. NO. 685,160 of 1901.
Machinery developed for the commercial manufacture of such units inserted axially compressed springs between the plies of a strip of sheeting folded in half longitudinally, and then seamed the folded strip along its edges, and transversely between the springs, to form pockets each enclosing a single spring. After re-expansion, the springs were turned in their pockets, resulting in a continuous strip of axially parallel springs with the marginal flaps of the edge seams of the fabric strip located at the same one end of all of the springs. The sewn seam version is typified by U.S. Pat. No. 1,813,993 to John F. Gail, and the welded seam version of thermally weldable pocket sheeting by my prior U.S. Pat. No. 4,489,977.
When strips of such springs are assembled by the usual methods in rows in which the springs are axially parallel, the seamed edges of the fabric are found on the same face of the assembly, which some experts have concluded contributes an undesirably different feel to opposite sides of a mattress embodying such an assembly, due to the presence of the upstanding seam margins of the fabric strip on the outside of the closing seam of the fabric. While the validity of that proposition may smack of the fairy tale of the princess and the pea, it has sufficiently engaged the interest of bedding manufacturers to promote the development of pocketed springs in strips in which the closure of the longitudinally folded fabric strip occurs along one side of the strip of pocketed springs rather than at the ends thereof. One example is provided by my U.S. Pat. Nos. 4,854,023 and 4,986,518, to which subsequent improvements are suggested by U.S. Pat. No. 5,613,287, St. Clair et al., and U.S. Pat. No. 5,749,133, Mauldin et al.
The reality, however, is that that approach, for whatever reason, failed to supplant the widely used spring-end closure seam that remains standard today.